Depending on the way you perform upgrades (freebsd-update or building from source) you may be interested in features that were added in the 10.1 release of FreeBSD for ZFS. The following options were added with the latest stable release of FreeBSD:
spacemap_histogram</b>
This features allows ZFS to maintain more information about how free space is organized within the pool
enabled_txg
Once this feature is enabled ZFS records the transaction group number in which new features are enabled.
hole_birth
This feature improves performance of incremental sends (zfs send -i'') and receives for objects with many holes. The most common case of hole-filled objects is zvols.
extensible_dataset
This feature allows more flexible use of internal ZFS data structures, and exists for other features to depend on.
embedded_data
This feature improves the performance and compression ratio of highly-compressible blocks. Blocks whose contents can compress to 112 bytes or smaller can take advantage of this feature
bookmarks
This feature enables use of the zfs bookmark subcommand.
filesystem_limits
This feature enables filesystem and snapshot limits.
You can validate whether your zpool can be upgraded by running “zpool status” and observing the following output:
status: Some supported features are not enabled on the pool. The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done, the pool may no longer be accessible by software that does not support the features. See zpool-features(7) for details.
You can view zpool-features(7) at the FreeBSD site: https://www.freebsd.org/cgi/man.cgi?query=zpool-features&sektion=7&manpath=FreeBSD+10.1-stable
It is important to note that any software that does not support these features may have issues once you run the upgrade.
If you are certain that you will not have any issues, you can simply upgrade your zpools by running the following command (in this example, I am upgrading my bootpool):
# gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada0
(This was required before I could run zpool upgrade)
# zpool upgrade bootpool
This system supports ZFS pool feature flags.
Enabled the following features on 'bootpool':
spacemap_histogram
enabled_txg
hole_birth
extensible_dataset
embedded_data
bookmarks
filesystem_limits
Bookmarks and filesystem_limits will be useful features for managing your ZFS datasets.